Electrical system for secret transmission



April 8, 1930. J. c. STEINBERG ELECTRICAL SYSTEM FOR SECRET TRANSMISSIONFiled Oct. 18, 192'? ooowon 2 co m QQN Q mm m M mummn;

/M/N7'0/P JUHN [I STE/Mama 5r 1 TTORAfEY Patented Apr. 8, 1930 JOHN C.STEINBERG, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 BELL TELEPHONELABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK ELECTRICAL SYSTEM FOR SECRET TRANSMISSION Application filed October'18, 1927. Serial No. 226,857.

This invention relates to transmission sys-. tems and particularly tothe method of and means for providing secrecy in the transmission ofmessages over said systems.

Systems for obtaining secrecy in signaling have heretofore been devisedwherein the messages are obscured or rendered unintelligible, whenreceived in the usual manner, by combining therewith noise frequencies.

This invention is based on this general principle, but the method of andmeans for generating the noise frequencies and their application to themessage waves is accomplished in a novel manner.

This invention operates upon the princi ple that message waves may bemasked or rendered unintelligible by applying to the ear of the listenerat the proper instant, noise waves of the proper frequency andamplitude. Toprovide the proper frequency and instant of application ofthe noise waves, they are generated by the action of the messagecurrents and impressed upon the transmission medium simultaneously withthe message currents. No message waves can, therefore, be impressed onthe transmission medium without their accompanying noise frequencywaves, the latter varying in amplitude in substantially directproportion with the amplitude of the message waves. I

It is an object of this invention to simplify the means for renderingmessages unintelligible to persons unauthorized to receive them andsimplify intelligible reception of messages by authorized persons.

A feature of this invention is the generation of the noise frequenciesby the action of the message waves for combination with the messagewaves.

Another feature of the invention is the varying of the, amplitude of thenoise frequencies in direct proportion to the amplitude of the messagewaves.

These objects and features and various advantages of this invention willbe more fully understood in the following detailed description taken inconnection with the accompanying drawing, the single figure of whichshows a two way system embodying the in vention.

applying to the station operated for receiv- In the secrecy apparatus ofthis invention, as shown in the drawing, is a transmitter 8, the circuitof which is through energizing battery 9 and the primary of afour-winding transformer 10. Signals are received on a receiver 12 incircuit with the secondary of a three-winding transformer 13. Thetransformer 10 has three secondary windings, 15, 16 and 17, thesecondary winding 15' being connected to the actuating winding of avoice operated relay 19. In series with this latter circuit is acondenser 20, and in shunt thereto an inductance 21 for the purpose ofmaking the relay more sensitive to the average voice frequency currents.

The secondary winding 17 is in circuit with a winding 23 of transformer13 and a winding 26 of transformer 27. The secondary winding 16 is incircuit with the lower armature of relay 19, filter F harmonic generatorHG, filter F winding 29 of transformer 30, and the upper armature ofrelay 19. Mes sage and" noise frequency currents are impressed on, andreceived from a line L through winding 31 of transformer 30 and winding28 of transformer 27. Across secondary 16 is shunted a variableresistance element 33 for varying the input into the harmonic generatorHG. This harmonic generator may be avacuum tube rectifier such asdisclosed in Patent No. 1,4463 52, February 27, 1923, and the filters Fand F may be of the well known unbalanced type such as shown in PatentNo. 1,227,113, May 22, 1917.

The operation of station A, the apparatus of which is set fortransmitting is as follows: Voice frequency currents from transmitter 8are impressed on secondary windings 15,16 and 17. The energy impressedon winding 15 operates the relay 19 and places the armatures thereof inthe position shown in the drawing. The energy impressed on winding "17passes onto the line L through transformer 27. The ener y impressed onwinding 16 passes by way 0 the lower armature of relay 19 to the filterF This filter is constructed to pass only frequencies between 200 and300 cycles per second. It is known that within this frequency range thefundamental of the female voice and the second harmonic of the malevoice are to be found, so that this voice frequency reaches the harmonicgenerator-HG. The energy of this frequency wave depends upon theamplitude of the voice waves but it is always large enough to generatesufficient harmon-.

ics to mask the voice waves. As filter F has a range of 500 to 2000cycles, only those har monics lying within this range are passed ontothe line L through transformer 30 by way of the upper armature of relay19.

This combination of voice and. noise frequency currents inunintelligible form may be transmitted between the two stations shown inany well known manner, for example, by the line L directly or bymodulating a high frequency carrier wave with the lower frequencies forradio or wired transmission. In the case of radio transmission the lineL would not of course, extend between the two stations but may beconsidered as leading from each station to suitable radio transmit tingand receiving apparatus.

, The operation of station B which is shown in condition to receive isas follows: The combination of message and voice frequencies is receivedon line L either directly in the case of radio or carrier transmission,or, from a suitable receiver, and impressed on transformers 27 and 30.From transformer 27 the unintelligible voice and noise frequencycurrents are impressed on transformer 13' through wind1ngs26 and 23'.However, part of the energy from the line L passes through transformer30 by way of the lower armature of relay 19' to filter F Since thefilters used in this system are of the-unbalanced type, the lowerterminal of winding 29 is common with one input terminal of filter F sothat the output of transformer'30' is impressed directly on filter FFrom this part of the received energy only the first harmonic of themale or the fundamental of the female voice frequency currents is passedby the filter F to the harmonic generator HG as in the case of F atstation A. This generator produces the same harmonics as generator HG atstation A and the filter F passes the same number of harmonics as filterF so that we have the same output waves at filter F as at filter F ofthe upper armature of relay 19. These noise frequencies are, however,impressed on this winding 180 out of phase with those arriving inwinding 23. This is accomplished by winding the turns of winding 24: inthe opposite sense to those of winding 23'. There is, therefore, aneutralization of the noise components in'the transformer 13 and theonly energy impressed on the secondary winding of this transformer .isthat of the message frequency waves generated in transmitter 8. Themessage is thus impressed on receiver 12' in intelligible form. Delaynetworks may also be employed in the output circuits of filters F and Eto obtain the necessary phase opposition for neutralizing the maskingnoise requencies.

The invention is also susceptible to various other modifications andadaptations and accordingly is not to be considered as limited in anyway by this particular disclosure.

What is claimed is:

1. In a signaling system, a source of mes sage waves, means forgenerating from said message waves noise waves having harmonics of saidmessage waves, means for combining said noise waves with said messagewaves, and means at a distant receiving point for neutralizing saidnoise waves while retaining the message waves.

2. Ina signaling system, a source of message waves, a source of noisewaves, a common output path for both of said sources, said output pathbeing connected to said source of message waves, means included in saidsource of noise waves for producing said noise waves from said messagewaves, and means for combining said noise and. message waves, said lastmeans comprising a relay operated by said messagewaves.

3. In a signaling system, a source of message waves, a source of noisewaves, a common output path for both of said sources, said outputpathbeing connected to said source of message waves, a harmonicgenerator for producingharmonics as noise waves from said message waves,said generatorbeing included in said sourceof noise waves inter posedbetween said source .of message waves and said output path, and means ata dismessage waves.

4. In a signaling system, a source of message waves, an output pathconnected to said source of message waves, a source of noise waveslnterposed between sa1d source of message waves and said output path,said source' of noise waves comprising a harmonic generator forproducing noise waves which are harinonics of one of saidmessage waves,and a relay associated with said source of message waves for connectingsaid source of message waves to said source of noise waves.

5. In a secrecy system, a source of message frequency currents, a sourceof noise frequency currents, a harmonic generator controlled by theimpression said message frequency currents thereon included in saidsource of noise frequency currents, an output path common to said noisefrequency currents and said message frequency currents, and a voiceoperated relay actuated by said source of message frequency currents formaking said system adaptable for combining and transmitting said messageand noise frequency currents in unintelligible form and for controllingthe impression of said message frequencycurrents on said harmonicgenerator.

6. In a secrecy system, in accordance with claim 5 in which said voiceoperated relay makes said system adaptable for receiving saidcombination of noise and message frequency currents or adaptable forcombining said message and noise frequency currents and transmittingsaid combination thereof.

7. In a secrecy system, a source of message frequency currents, a sourceof noise frequency currents, means for combining said message and noisefrequency currents, and means included in said source of noise frequencycurrents for selecting one frequency of the message currents, forgenerating from said one frequency, harmonics thereof for masking saidmessage frequency currents, and means for eliminating the efiect of saidharmonic frequency components from the mes: sage waves aftertransmission of the message waves and the noise waves to a distantpoint.

8. A method of masking intelligible message waves,-comprising first,selecting a component of said Waves, second generating harmonies fromsaid component, and third combining said harmonics and said messagewaves in a common output path.

9. In a transmission system, an incoming line in which there is anunintelligible combination of message and noise frequency currents,receiver means on which said combination. is impressed, and a secondmeans on which said combination is impressed, said second meansgenerating from saidmessage currents the same noise frequencies ascontained in said combination and impressing them on said receiver meansin phase opposition to said noise frequency currents in said 11. Atransmission system in accordance with claim it) which said receivermeans com rises a three "winding transformer, said com ination beingreceived on one winding thereof, and said noise harmonics being receivedon a second winding thereof, said second Winding being reversed withrespect to said first mentioned winding.

12. la a signaling system, a source of message waves, means forgenerating noise Waves under control of said message waves, and a commonoutput path for said message and said noise waves, said generating meansincluding a harmonic generator for producing noise representingharmonics of a component of said message waves, the amplitudes of saidharmonics being proportional to said component of said message Waves,and means for removing the harmonic frequency waves from the messageWaves.

In witness whereofi I hereunto subscribe my name this 17th day ofOctober, A. D., 1927.

JOHN C. STEINBERG.

